This invention relates to a method for use in coiled tubing operations wherein fatigue of the coiled tubing owing to short trips is reduced.
Coiled tubing is increasing in popularity as a method of drilling wells or conducting operations in an oil or gas wellbore. Coiled tubing is used as a continuous strand and is therefore easier and faster than conventional pipe in many applications involving well drilling or well bore operations, such as drilling wells, deploying reeled completions, logging high angle boreholes, and deploying treatment fluids. Coiled tubing is particularly useful in horizontal or multi-lateral wells.
Conventional coiled tubing operation equipment typically includes coiled tubing spooled on a reel, an injector to run coiled tubing into and out of a well, a gooseneck affixed to the injector to guide the coiled tubing between the injector and the reel, a control cab with the necessary controls and gauges, and a power supply. Additional or auxiliary equipment also may be included.
Typically, the coiled tubing is shipped, stored, and used on the same coiled tubing reel. Coiled tubing reels are deployed from trucks or trailers for land-based wells and from ships or platforms for offshore wells. When spooling or unspooling coiled tubing on a reel, the tubing is subjected to bending forces that can damage it. These bending forces cause tubing fatigue, and this fatigue is a major factor in determining the useful life of a coiled tubing work string.
Various injectors are known to handle various diameters of coiled tubing. A typical gooseneck injector comprises a curved guide member, with the curve extending in an arc of approximately ninety degrees (90xc2x0) or more and an injection head comprising a drive motor, drive chain(s), chain tensioners, and a weight indicator. These gooseneck injectors typically include a plurality of rollers for supporting and constraining the tubing while it is being guided along the curved guide member into the injector. The chain tensioners maintain effective traction between the chain and coiled tubing and permit movement of the coiled tubing into and out of the wellbore as controlled by the injector.
Coiled tubing reels typically rely on hydraulic power to operate the reel drive, brake, and spooling guide systems. Most coiled tubing reels can be powered in xe2x80x9cin-holexe2x80x9d[i.e. running-in-hole (RIH)] and xe2x80x9cout-holexe2x80x9d[i.e. pulling-out-of-hole (POH)] directions. The reel drive and its associated motor provide the reel back-tension, that is the tension in the coiled tubing between the reel and the injector that is used to spool and unspool the tubing on the reel and prevent tubing sagging between the reel and the injector while running coiled tubing into or out of the wellbore. The coiled tubing back-tension can be generated by either the reel or the injector or both. Typically, reel brake systems are self-actuated by an internal spring that requires air or hydraulic pressure to operate the brake release. In conventional operations, the reel brake generally is applied whenever the tubing is stationary. Applying the reel brake prevents the coiled tubing reel from rotating but it does not prevent the coiled tubing on the reel from unwinding owing energy that is stored in the coiled tubing while it is spooled on the reel. Even if the reel brake is applied and the reel is stationary, the coiled tubing can move or unwind if the coiled tubing back-tension is released.
The spooling guide system, commonly known as a levelwind assembly, guides the coiled tubing onto the reel by sensing the motion of the reel and moving the upper free end of the guide arm. Often, some vertical adjustment of levelwind assembly is necessary to achieve the desired angle of the coiled tubing to the reel. The levelwind system has the ability to move left and right (in the general horizontal direction) and up and down (in the general vertical direction). Typically, the vertical movement is controlled manually and the horizontal movement is controlled automatically, with a manual override for small horizontal alignment corrections. It is known to pivot the entire levelwind assembly on the reel support frame to allow the levelwind head to suit the angle at which the tubing leaves the reel.
It is necessary that coiled tubing have sufficient strength to conduct operations downhole without failure or buckling while being flexible enough to be spooled onto a coiled tubing reel. The high section modulus of coiled tubing is advantageous as to its strength and buckling characteristics but is disadvantageous as to its ability to be spooled on a reel. That is, properties that make coiled tubing perform well downhole work to a disadvantage when attempting to spool coiled tubing on the surface of the ground. One such disadvantage of the high section modulus is that high level of energy is stored in the coiled tubing while it is spooled on the reel.
Coiled tubing is subject to strains owing to bending and straightening movements in each coiled tubing operation. The bending and straightening movements lead to fatigue and the coiled tubing must be replaced after a certain number of runs or trips down a well. Furthermore, the strains in coiled tubing may cause residual bends in the tubing which may prevent it from straightening properly in the borehole or rolling properly on the reel.
Coiled tubing passing downward (generally running-in-hole) undergoes at least three straining events: 1) as the coiled tubing is straightened upon leaving the reel and on approach to the gooseneck; 2) as the coiled tubing is curved over the gooseneck; and 3) as the coiled tubing is straightened on its way from the gooseneck to the injector head. Similarly, coiled tubing passing upward (generally pulling-out-of-hole) undergoes at least three straining events: 1) as the coiled tubing is extracted from the wellbore and curved over the gooseneck; 2) as the coiled tubing is straightened upon leaving the gooseneck and on approach to the reel; and 3) as the coiled tubing is being curved onto the reel. These numerous bending and straightening movements strain the coiled tubing and lead to fatigue.
The cost of coiled tubing represents a large expense in coiled tubing drilling and conventional coiled tubing operations. Fatigue is a major factor in determining the useful working life of a coiled tubing work string. Fatigue is a cumulative phenomenon that is not directly measurable and therefore must be predicted in determining useful working life of coiled tubing. Some factors that effect fatigue include number of feet run, bending cycles, bending radii, internal pressure, and material characteristics.
Studies have shown that notable damage to coiled tubing is caused by the fatigue strains that result from the repeated bending and straightening of coiled tubing at the reel, gooseneck, and injector head. Studies of the behavior and fatigue of coiled tubing have shown that the useful life of coiled tubing string is largely determined by fatiguing events outside the wellbore, that is, the coiled tubing handling methods at the surface. In particular, damage is caused by the repeated bending and straightening of the coiled tubing at the gooseneck and reel. What is needed is a system that reduces the fatigue in coiled tubing by reducing the number of bending and straightening events that coiled tubing undergoes to accomplish a particular wellbore objective.
WO 98/14686 discloses a tubing reel and a tubing reel injection system that can be tilted about an axis to maintain a desired arch of the tubing between the reel injector and the main surface injector. A forty-five feet (45xe2x80x2) arch radius is considered desirable. The arch is maintained throughout the coiled tubing operation, and the tubing is spooled and unspooled from the reel when the tubing is moved in the well.
In the Transocean unit described in U.S. Pat. No. 6,092,756 entitled xe2x80x9cSupport of a combined feed-outfeed-in device for a coilable tubingxe2x80x9d, the reel is mounted directly above the injector head. Coiled tubing bending cycles associated with the traditional gooseneck are eliminated but the coiled tubing is still spooled on and unspooled from the reel in the standard manner when the tubing is moved into or out of the well.
Some operations have used a floating vessel to perform coiled tubing operations where the coiled tubing was fixed in another location at the reel. In these applications, the coiled tubing undergoes reverse bending, that is the shape of the pipe profile between the boat and the injector has an xe2x80x9cSxe2x80x9d configuration. This reverse bending is detrimental because it increases fatigue in the coiled tubing . Furthermore, these operations are not suitable for use on land. During these operations the hold-down rollers on the gooseneck are engaged, the coiled tubing conforms to the gooseneck curvature, and the coiled tubing is subjected to the bending cycles on the gooseneck.
WO 00/08296 relates to tubing injector for moving tubing into and out of a wellbore. The system uses matching sets of engagement assemblies to grip the tubing and produce a lateral latched arrangement around the tubing. The assemblies then move the tubing through the use of a transport mechanism, such as a drive system of chains or sprockets. The injection system is used for continuous tubing, such as coiled tubing or jointed tubing. The tubing is still spooled on and unspooled from the reel every time the tubing is moved in the well.
The present invention is directed to a system to reduce the fatigue induced by small pipe movements, the system is referred to herein as a short trip module (STM). The system allows the reel to remain stationary while the main injector head moves the tubing. Short trips particularly occur in coiled tubing drilling/milling operations. These small coiled tubing movements create areas of high fatigue in some sections of the coiled tubing. These localized areas of high fatigue prematurely reduce the useable life of the entire coiled tubing string. Existing systems, which only reduce or eliminate bending events at the gooseneck, do not address fatigue induced by spooling and unspooling the tubing from the reel. What is needed is a system to reduce localized fatigue in coiled tubing both at the gooseneck and on the reel, in particular to reduce or eliminate the high localized fatigue induced by short trip movements of coiled tubing.
Initially, at the start of a job or required downhole operation, coiled tubing is run in the wellbore. In accomplishing wellbore operation, often a length of coiled tubing must be pulled out of the wellbore and subsequently run into the wellbore. Frequently the length of coiled tubing involved is short (typically less that 30 feet). These frequent short trips are repetitive and severely fatigue coiled tubing in localized areas.
It is an object of the present invention to provide a system and method to reduce the fatigue in coiled tubing caused by short trips, wherein said system comprises coiled tubing, a coiled tubing reel, a levelwind assembly, a coiled tubing brake, a tubing arch, and a main injector comprising a gooseneck and injector head. The present invention can be used in conjunction with both a conventional reel-gooseneck-injector system and a continuous arch system that includes a reel injector.
In one embodiment, the present invention provides a method to reduce the fatigue induced in coiled tubing by short trips in and out of the well during coiled tubing operations. A conventional reel-gooseneck-injector system is used, comprising a coiled tubing reel, levelwind, power source, injector head, gooseneck, control cab, and monitoring system. In the present invention, the hold-down rollers on the gooseneck of the conventional system are removed to allow the coiled tubing to gradually form an arch radius. Additionally, a coiled tubing brake is installed to regulate or stop the coiled tubing movement on the reel as required by the present invention. This coiled tubing brake is typically mounted on the levelwind and thus called a levelwind brake. The present method comprises: (i) applying the levelwind brake, thereby placing the coiled tubing on the reel in a stationary position during short trips, (ii) pulling the coiled tubing out of the hole or running the tubing in the hole with the main injector head, and (iii) adjusting the levelwind assembly to maintain the coiled tubing in an arch without reverse bending.
The method is used while the coiled tubing is in the wellbore, having been initially run into the wellbore using conventional methods known to those skilled in the art, and when a short trip of the coiled tubing is needed to accomplish a downhole operation. To initiate the short trip module, first a certain short length of coiled tubing must be pulled out of the wellbore by using the injector head without spooling the tubing on the reel. When pulling coiled tubing out of the wellbore, the method comprises applying the braking force of the levelwind brake to stop the coiled tubing reel from turning and prevent the coiled tubing on the reel from moving, while forming a tubing arch between the reel and injector head. The tubing arch does not exceed the maximum arch height in which the arch becomes unstable or interferes with surface equipment. The maximum arch height relates to the stability of the arch and depends on the equipment geometry, the coiled tubing dimensions, and environmental factors such as wind speed. If the maximum allowed arch height is exceeded, the levelwind brake is gradually released to allow the tubing to be spooled on the reel and continue pulling out of hole using normal spooling procedures.
When running coiled tubing into the wellbore during the short trip mode of operation, the tubing between the reel and the gooseneck is already in an arch form. The method then comprises activating the levelwind brake, adjusting the levelwind arm to maintain the coiled tubing in a gradually decreasing arch between the reel and the injector head; slowing the speed of the coiled tubing in the injector prior to contacting the gooseneck with the tubing; gradually releasing the levelwind brake; contacting the gooseneck with the coiled tubing; releasing the levelwind brake and adjusting the reel back tension to normal operating conditions; and continue running in hole using normal spooling procedures.
In another embodiment, the present invention further provides an automated system for controlling the various components and managing a tubing arch during the short trip mode of operation comprising a control system, a height sensor, monitors and relays of levelwind brake pressure, reel depth, reel back pressure, and a load cell.
In another embodiment, the present invention is used in conjunction with a continuous arch system, said system comprising a reel traction device. The method comprises (i) applying the reel traction device as a brake, thereby placing the coiled tubing on the reel and the coiled tubing reel in a stationary position; (ii) pulling the coiled tubing out of the hole and running the coiled tubing in the hole with the main injector head; and (iii) adjusting the levelwind assembly to maintain the coiled tubing in an arch form without reverse bending. The present invention may further comprise a reel traction control system to automate the application of the reel traction device.